With the development of multimedia technology, micro projection display devices are widely used inside cell phones, digital cameras, portable projectors and other handheld devices, for amplifying and projecting images.
FIG. 1 schematically shows a conventional projection display device, which mainly includes a light source device 10, an illumination system 11, a Polarization Beam Splitter (PBS) 12, a display panel 13 and a projector lens 14. A conventional display panel (Liquid Crystal Display) is a transmission-type display device, while an LCOS (Liquid Crystal on Silicon) is a reflection-type display device which reflects incident light to display images. The working principle of an LCOS display device is described here. A natural light beam is emitted by the light source device 10. The illumination system 11 receives the natural light, which is then transformed to parallel polarized light including p-polarized light and s-polarized light by the PBS 12. The PBS 12 forms an angle with respect to the first direction (x-axis), and transmits one of the two types of parallel polarized light and reflects the other. For example, the PBS 12 transmits the p-polarized light (polarized direction is parallel to the rays incident plane) and reflects the s-polarized light (polarized direction is vertical to the rays incident plane). The s- or p-polarized light are defined relative to the plane of incidence of the ray on the surface, which are not characteristics of the beam itself but just two types of parallel polarized light out of PBS in this invention. The s-polarized light is incident into the surface of the display panel 13, and is transformed to p-polarized light by the LCOS for being reflected back to the PBS 12. Since the PBS 12 transmits the p-polarized light, the p-polarized light passes through the PBS 12 and further into the projector lens 14. By amplifying, the projector lens 14 projects to the outside the image generated by the display panel 13.
A conventional projection display device only uses the reflected parallel polarized light from the PBS 12 to project image, and the transmitted parallel polarized light is wasted. Therefore, the light utilization efficiency is low, commonly less than 10%, which leads to a poor image quality under fixed-power of the light source device 10.
In the Chinese patent application No. 200910172326.1, aspherical lenses and cylinder lenses are adapted to adjust the light beam from a light source device before transmission, which generates a light spot matching the LCOS shape. This method improves the light utilization efficiency to a certain degree. However, since it provides a similar structure as shown in FIG. 1, which uses only one type of polarized light, the light utilization efficiency is still low.